The behavior of photochromic glasses during activation and bleaching is investigated. A two-state phenomenological model describing light-induced activation (darkening) and thermal bleaching is presented. The proposed model is based on first-order kinetics. We demonstrate that the time behavior in the activation process (acting simultaneously with the thermal fading) can be characterized by two relaxation times that depend on the intensity of the activating light. These characteristic times are lower than the decay times of the pure thermal bleaching process. We study the temporal evolution of the glass optical density and its dependence on the activating intensity. We also present a series of activation and bleaching experiments that validate the proposed model. Our approach may be used to gain more insight into the transmittance behavior of photosensitive glasses, which could be potentially relevant in a broad range of applications, e.g., real-time holography and reconfigurable optical memories.
© 2008 Optical Society of America
Original Manuscript: March 26, 2008
Revised Manuscript: June 3, 2008
Manuscript Accepted: June 11, 2008
Published: July 9, 2008
José A. Ferrari and César D. Perciante, "Two-state model of light induced activation and thermal bleaching of photochromic glasses: theory and experiments," Appl. Opt. 47, 3669-3673 (2008)